arduino mosfets and bipolars

[duxbuz]

Hi

I am trying to build circuit for arduino uno and small lego motor. Using 9v battery.

I have seen some examples of arduino circuits that don't use relays with motors they use bipolar transistors.

The one mentioned is a Tip120. When I search on my suppliers site I get two options:
https://cpc.farnell.com/jsp/search/...se&skipParametricAttributeId=&prevNValues=411

sorry for rubbish big link!

A 65mW and a 65W. Which should I choose?

I received more advice about using Logic level Mosfet. Can this be used the same way? With no relay just a diode?

Also when I search for logic level mosfets I searched for Vgs between 3.75 and 5v. Is this correct?

cpc website uk . shortened link
**broken link removed**

Which ones can I select to fit my small lego motor and 9v battery circuit?


Can anyone help me out?
Many thanks

 

[jiripolivka]

First get ready to experiments. There are many suitable BJTs and MOSFETs but some are best with more than 9VDC.
Measure the logic output voltage from your Arduino to a 3K load resistor, and build a logic voltage source from a 9V battery, with a SPDT switch. Test a logic MOSFET from your logic source, with the motor and 9V battery before you connect it to Arduino. Be sure to connect a protection diode across the MOSFET as the motor is an inductive load.
Make sure there is a large capacitor across the 9V battery (like 1000 uF) to protect Arduino from voltage kicks the motor can generate.
BJTs have much larger resistance when open, a heat sink is needed. I would use one for the MOSFET, too. When the motor stalls, the current peaks high. Maybe your 9V battery will not live long to feed the motor.